A theory of acoustic invariance claims that the universal set of phonetic features used in natural language can be characterized by invariant properties derived directly from the acoustic signal, that the perceptual mechanism is specifically tuned to extract these properties, and that they form the primary perceptual attributes used in ongoing speech perception. The current research attempted to assess this model by 1. assessing whether at some stage of the perception process invariant properties residing in the short-time spectrum are in fact perceived independent of context-dependent cues as absolute onset frequency, formant motions, and vowel context; 2. exploring further the acoustic characteristics of onsets to ascertain if the gross shape of the onset spectrum optimally captures the properties for place of articulation; 3. developing a theory of acoustic invariance in relation to a broader framework than originally elaborated.